NEW: Annual Report - George Mason University

Photosynthetic Rate (mgC/L/hr)
600
500
400
300
200
100
Gunston Cove Study - 2003
Station 7
Station 9
0
Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
27
Chlorophyll a measures the
standing crop of phytoplankton
while photosynthetic rate
measures their productivity.
Phytoplankton are primary
producers meaning that they
take CO2 and sunlight and
create living tissue by the
process of photosynthesis. This
can then serve as food for
animals and other living things.
Since light is a factor in
photosynthesis and light varies
in the environment,
measurements are made in the
lab under ideal light conditions
so that these rates can be
compared between samples.
Figure 31. Photosynthetic Rate at Light Saturation (ugC/L/hr). Month tick is at first day
of month.
Photosynthetic rate followed patterns similar to those in chlorophyll a (Figure 31). In the
cove there was a gradual increase reaching a seasonal peak in August and early
September. A major decline was observed in late September with the passage of
Hurricane Isabel. In the river the spring peak was apparent and the seasonal maximum
occurred in August and early September followed by the Isabel decline. Photosynthetic
rate per unit chlorophyll (P B max) was generally from 3-10 mgC/mgChla/hr. Exceptions
were several high values in the river in spring and early summer.
PBmax (mgC/mgChla/hr)
25
20
15
10
5
Gunston Cove Study - 2003
Station 7
Station 9
0
Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
Figure 32. P B max (mgC/mgChla/hr). Month tick is at first day of the month.
Photosynthetic rate is a function
not only of light but of the
amount of phytoplankton
present. To get a measure of the
rate that accounts for differences
in the total amount of
phytoplankton in the water, we
can determine how much living
tissue is created per unit of
chlorophyll. This could be viewed
as a measure of growth
potential.